Various proposals, such as mentioned below, have been made on the method of producing the carbon particles in recent years.
(1) The core/shell particles of polymethyl methacrylate (PMMA)/polydivinylbenzene (PDVB) are made by polymerization and carbonized to form the hollow carbon particles (Non-Patent Document 1).
(2) The submicron-sized silica particles having a hard core/mesoporous shell structure are made, and by using them as its prototype mold, a phenolic resin or polydivinylbenzene is polymerized in situ. After carbonization, the silica prototype mold is removed (Its prototype mold method 1) (Non-Patent Document 2).(3) A polymer shell is formed on the surface of colloidal silica, and after carbonization, silica in the shell is dissolved to make the hollow carbon particles (Its prototype mold method 2) (Non-Patent Document 3).
The method of (1) mentioned above is capable of making the particles with a size on the order of 15 nm, but the carbon particles obtained by this method are amorphous with 2θ=24° as determined by X-ray diffractometry (XRD). The proposals of (2) and (3) are the method in which the material is shaped in conformity to the mold, and the shell of the carbon particles obtained from the method of (2) has a mesoporous structure. Although there is no report relating to crystals, it is considered that the development of crystal structure has been neglected because of the advancement of porous structure. Also, these particles are of a spongy structure having mesopores in the surface. According to the method of (3), since divinylbenzene, a crosslinking agent, is used as polymer, it is considered difficult to develop a crystal structure with the obtained carbon particles, because generally it is supposed that the crystal structure can hardly be developed since polydivinylbenzene is carbonized through a solid-phase carbonization reaction.
In addition to the above-mentioned, there has also been reported a carbon particle called “nanopolyhedron particle” (Non-Patent Document 4). This carbon particle has a telescopic structure comprising a pile of several to several ten layers of graphite, presenting a polyhedral configuration as a whole. Just as it is difficult to disperse the carbon nanotubes in a solvent, it is so much difficult and requires much labor and cost to obtain a uniform dispersion of the nanopolyhedron particles. Also, since these nanopolyhedron particles present a polyhedral configuration, they are low in sphericity and poor in uniformity of shape.
There has also been reported a method for obtaining the fibrous carbon particles (carbon nanofibers) using an alumina membrane having pores of 100 nm in diameter and 60 microns in length, in which a heated mesophase pitch is flown into the said pores as a capillary flow and, after particle carbonization, the its prototype mold is dissolved away (Non-Patent Document 5). According to this method, however, since the alumina membrane takes a cylindrical configuration, although it is possible to provide the fibrous carbon particles, it is impossible to create the spherical carbon particles which are perfectly spherical or have a high degree of sphericity.
The carbon spherules having substantially a uniform configuration and a sharp particle size distribution, and a method of producing such carbon spherules have also been reported (Patent Document 1). However, it can be seen from the presented drawings (electron micrographs) that the structure of these carbon spherules has no void in the inside. If a void exists in the inside of the spherule, then the contrast should differ between the peripheral portion and the inside of the particle.
Non-Patent Document 1: Chem. Mater., pp. 2109-2111, Vol. 15, No. 11, 2003
Non-Patent Document 2: Adv. Mater., pp. 19-21, 2002, 14, No. 1, January 4
Non-Patent Document 3: Adv. Mater., pp. 1390-1393, 2002, 14, No. 19, October 2
Non-Patent Document 4: Chemistry and Physics of Fullerene, p. 235, Mar. 15, 2002, published by Nagoya University Publishing Society
Non-Patent Document 5: Adv. Mater., pp. 164-167, 2003, 15, No. 2, January 16
Patent Document 1: Japanese Patent Application Laid-Open (KOKAI) No. 2004-211012